A relaxed and upbeat Barack Obama invoked the spirit of Martin Luther King Jr. and lavished praise on two prominent Republicans in calling for a new spirit of bipartisanship.

After visiting wounded veterans and helping volunteers paint a dorm for homeless teens in Washington, Obama dashed to three black-tie dinners Monday night. One honored Sen. John McCain, the Republican he defeated in November, and another honored Colin Powell, who was secretary of state for President George W. Bush.

The third dinner was for Joe Biden, who will take the vice presidential oath of office before Obama becomes president on the Capitol steps Tuesday.

Obama called McCain and Powell American heroes who set standards of patriotism and bipartisanship for all to follow.

He hugged McCain onstage and called for Americans’ help "in making this bipartisan dinner not just an inaugural tradition, but a new way of doing the people’s business in this city."

Throughout the day, Obama showed no hints of nervousness about becoming president within hours.

"I don’t sweat," he told volunteers at Sasha Bruce House, a shelter for homeless teens in one of Washington’s poorer neighborhoods. "You ever see me sweat?"

All day, he switched easily from self-deprecation to faux cockiness to calls for action.

"Make sure I do something simple," he told Sasha Bruce organizers. "Don’t give me plumbing or electrical work."

As he painted a wall with a roller brush, he quoted King as saying, "Everybody can be great because everybody can serve."

"Right?" he asked the late civil rights leader’s eldest son, Martin Luther King III, who was almost overlooked while painting nearby.

"Right," King assured the president-elect.

Obama made a pitch for community service, his theme of the day.

"Given the crisis that we’re in and the hardships that so many people are going through," he said, "we can’t allow any idle hands."

But when onlookers pushed the earnestness too far by excessively praising Obama’s painting skills, he pushed back.

"It’s not rocket science," he said with a smile. "You take the pole and the roller, then you roll."

The day’s most somber note came early, away from cameras. Obama spent about 80 minutes visiting 14 wounded veterans of the Iraq and Afghanistan wars at Walter Reed Army Medical Center, where journalists were kept away.

At lunchtime, he and his wife, Michelle, greeted several hundred people writing letters to U.S. troops and undertaking other volunteer tasks at a Washington high school.

A few miles away, thousands of people streamed into downtown Washington and the National Mall, a prelude to the massive crowds expected Tuesday. They represented every age, race and region of the country, but Obama spent much of Monday in some of Washington’s most heavily black neighborhoods.

Hundreds of people stood on their sidewalks and front porches to wave and shout as his motorcade whizzed past.

As he did throughout his campaign, Obama made little or no overt references to race, emphasizing instead the ties that bind all Americans.

"This country is great because of its people," he said at Sasha Bruce House. "Don’t underestimate the power for people to pull together and to accomplish amazing things."